Cathode ray tube arrangement utilizing magnetic shunts for controlling color registration

ABSTRACT

A control apparatus for a cathode ray tube of the shadow mask type has magnetic shunts movable in field-distorting proximity to electromagnets provided to influence magnetically the pole pieces associated with the electron guns of a cathode ray tube to which the apparatus is fitted. The apparatus includes a main beamdeflecting yoke. Each electromagnet is connected electrically in series with the beam-deflecting yoke.

Uted States Patent Rogers Feb. 20, 1973 CATHODE RAY TUBE ARRANGEMENT [56] References Cited UTILIZING MAGNETIC SHUNTS FOR UNITED STATES PATENTS 2,743,389 4/1956 Giuffrida ..3 15/13 C 2,880,367 3/1959 Caprio ..3 15/13 C 3,305,744 2/1967 Werst ..335/2l2 3,002,120 9/1961 Clay ..3l5/l3 C 75 I Inventor: B h J Rogers London 3,414,758 12/1968 Grue ..3l5/l3 C gland Primary ExaminerCarl D. Quarforth [73] Assignee: The Rank Organisation Limited, Assistant Examiner.|. M. Potenza London, England Attorney-Griffin, Branigan and Kindness [22] Filed: May 14, 1970 [57] ABSTRACT [21] Appl. No.: 37,139

Int. Cl. ..H0lj 29/50 Field of Search ..335/2l2; 315/13 C A control apparatus for a cathode ray tube of the shadow mask type has magnetic shunts movable in field-distorting proximity to electromagnets provided to influence magnetically the pole pieces associated with the electron guns of a cathode ray tube to which the apparatus is fitted. The apparatus includes a main beam-deflecting yoke. Each electromagnet is connected electrically in series with the beam-deflecting yoke.

' 3 Claims, 3 Drawing Figures PATENTED H82 Km 3', 7 1. 7. 788

INVENTOR BERNHARD JOHN ROGERS BY Mm, mgw a Huidn m ATTORNEYS CATIIODE RAY TUBE ARRANGEMENT UTILIZING MAGNETIC SHUNTS FOR CONTROLLING COLOR REGISTRATION This invention relates to control apparatus for cathode ray tubes of the shadow mask type as used in color television receivers.

A shadow mask television tube as at present constructed contains several electron guns, one for each of the different components, e.g., the color components, of the picture, grouped around and offset from the central axis of the tube. With this arrangement means must be provided for correcting the shape of the raster produced on the screen by each gun otherwise, as a result of the non-axial positions of the guns, the respective rasters will suffer geometrical distortions of substantially parabolic or tilted form with consequent lack of registration of the color images.

It is already known to provide a shadow mask color television tube incorporating means for correcting the shapes of the rasters produced by the different guns, such means consisting of internal pole pieces integral with the guns, and external horseshoe form electromagnets one for each pole piece, each located to excite magnetically the associated pole piece, the electromagnets being arranged to be energized by current derived from constant current or constant voltage sources, these current being adjustable in amplitude and shaped to particular waveformv The means for adjusting the amplitudes of the exciting currents normally takes the form of potentiometers, and the shape of the waveforms is determined by the influence of the inductances of the electromagnets with an adjustable correction obtained by potentiometers and/or additional and variable inductances. This form of raster shape correction requires a large number of potentiometers with the attendant complication and difficulty of obtaining the best settings for all the potentiometers and variable inductances where fitted. The task to be performed is to provide a means of control which will allow the number of components requiring adjustment to be reduced. It is an object of the present invention to provide a control apparatus which is simply and easily adjusted. It is also an object of the invention to provide the apparatus as a unit assembly which can be supplied ready for fitting to a television tube. It is a further object of the invention to provide a cathode ray tube incorporating such an apparatus.

According to the invention a control apparatus for a cathode ray tube of the shadow mask type having several electron guns offset from the central axis of the tube and a pole piece, integral with each electron gun incorporates an annular main beam-deflecting yoke formed to fit around a cathode ray tube, and electromagnets, one for each pole piece so located that they are in magnetic proximity to respective pole pieces when the apparatus is fitted to the tube, and is characterized in that each electromagnet is connected electrically in series with the beam deflecting yoke, and magnetic shunts are movable in field-distorting proximity to the electromagnets.

In a cathode ray tube having three electron guns corresponding with blue," green" and red" signals the electrogmagnet associated with the blue gun normally requires twice the excitation current of the red and green electromagnets. As the main beamdeflecting yoke normally incorporates two parallelconnected scanning inductances the electromagnet intended to be associated with the blue" gun may be connected in series with the two parallel-connected scanning inductances and the two already series-connected electromagnets intended to be associated with the red and green guns may be connected in series with one of the two parallel-connected inductances.

Each magnetic shunt may be constituted by a bar of paramagnetic or diamagnetic material.

The leading end of the bar may be tapered.

In the normal shadow mask television tube having blue," red and green guns these are located around the central axis of the tube. In such a cathode ray tube it is normal to position one gun, usually the blue gun, vertically above the central axis of the tube and the red and green guns below and diagonally displaced on each side of the central axis of the tube. A control apparatus for such a tube may incorporate a single magnetic shunt for the electromagnets intended to be associated with the red" and the green guns. The shunt may be movable circumferentially.

The shunts are preferably arranged to be movable axially of the yoke.

A practical embodiment of the invention is illustrated in the accompanying drawings in which FIG. 1 is a diagrammatic representation of a color projection cathode ray tube fitted with a control apparatus according to the invention,

FIG. 2 is an electrical diagram showing how the appropriate currents for the several electromagnets are obtained, and

FIG. 3 is a view looking axially of the tube of FIG. 1 showing diagrammatically the blue, green and red projection guns and the magnetic shunts positioned in relation to the electromagnets associated with the guns.

In the drawings 1 denotes a cathode ray tube, 2, 3 and 4 denote electron guns with their pole pieces, the guns 2, 3 and 4 being respectively responsive to blue, green and red signals, 5, 6 and 7 denote electromagnets located externally of the tube 1 and in magnetic proximity to the pole pieces of the respective electron guns 2, 3 and 4. 8 denotes a beam-deflecting yoke, 9 and 10 denote magnetic shunts constituted by bars of material capable of distorting an applied magnetic field, the leading ends of the bars being tapered at 9A. The control apparatus is constituted by the electromagnets 5, 6, 7, the beam-deflecting yoke 8 and the magnetic shunts 9 and 10. The shunt 9 is associated with the electromagnet 5 and the shunt 10 is associated with the electromagnets 6 and 7. The two shunts 9 and 10 are movable longitudinally of the axis of the yoke and of the tube into the gap between the electromagnets 5, 6 and 7 and the pole pieces 2,3 and 4, while the shunt 10 is additionally movable circumferentially of the yoke and of the tube. Referring particularly to FIG. 2, 11 and 12 denote two parallel-connected inductances constituting the beam-deflecting yoke, the electromagnets 5 .being connected in series with both inductances 11 and 12, while the electromagnets 6 and 7 connected in series with one another are connected in series with the inductance 12.

In practice, the control apparatus 5,6,7 ,8,9,l0 is preferably constructed as a unit assembly. Each unit assembly may be specially designed for operation with a particular commercially available cathode ray tube. In operation movements of the magnetic shunts 9 and in magnetic proximity to the electromagnets 5, 6 and 7 has the effect of distorting the magnetic fields of the electromagnets 5, 6 and 7 and thus altering the magnetic effect of the electromagnets on the pole pieces of the electron guns 2, 3 and 4 whereby to change the degree of influence of the pole pieces on the electron beams emitted by the guns 2, 3 and 4. The taped ends 9A of the shunts permit more gradual adjustment to be made in the change of magnetic effect of the electromagnets on the pole pieces, thereby facilitating control. The use of a single magnetic shunt 10 associated with the electromagnets 6 and 7 and the pole pieces of the guns 3 and 4 facilitates adjustment of the red and green rasters because the electromagnets 6 and 7 provide corrections of the associated beams in diagonal directions towards and away from one another along radial paths, and the simultaneous correcting effect of the single shunt 10 on the two beams together with the differential effect on the two beams provided by moving the shunt l0 circumferentially provides a relative correcting motion of red to green rasters which is substantially horizontal or vertical. Adjustment of the color rasters is thus rendered simple. Synchronization of the fluctuations of the currents flowing through the electromagnets with the scanning movements of the beam is assured by the direct incorporation of the electromagnets in the circuit of the beam-deflecting yoke so that simple fixed resistance/capacity networks are sufficient to achieve exactly the waveforms desired. With one resistance/capacity network for the blue beam and one common resistance/capacity network for the red and green beams it will be understood that complete control of the waveforms of the control currents is provided by two potentiometers, one in each network. Control of the amplitudes of the control currents is provided by a simple mechanism providing independent longitudinal movement of both shunts, and

additionally circumferential movements of the shunt associated with the red" and green" electromagnets.

What is claimed is:

1. Control apparatus for controlling a cathode ray tube of the shadow mask type having several electron guns offset from the central axis of the tube, and a magnetic pole piece integral with each electron gun, comprising an annular main beam deflecting yoke formed to fit round the cathode ray tube; electromagnets, one for each pole piece, so located that they are in magnetic proximity to their respective pole pieces when the apparatus is fitted to the tube, the electromagnets being connected electrically in series with the beam deflect ing yoke; and magnetic shunt members movable in field distorting proximity to each of the electromagnets, each shunt member comprising a bar of paramagnetic or diamagnetic material having a tapered leading end.

2. Control apparatus for controlling a cathode ray tube of the shadow mask type having three electron guns spaced round and offset from the central axis of the tube so that, considering one gun as directly above the central axis of the tube, the other two guns are below and on different sides of the central axis, and a magnetic pole piece integral with each electron gun,

comprising an annular main beam deflecting yoke formed to fit round the cathode ray tube; electromagnets, one for each pole piece, so located that they are in magnetic proximity to their respective pole pieces when the apparatus is fitted to the tube; and two magnetic shunt members one associated with the electromagnet of the gun above the central axis of the tube and the other associated in common with the electromagnets of the other two guns, both shunt members being movable in field distorting proximity to the associated electromagnets.

3. Control apparatus as claimed in claim 2, in which both shunt members are movable axially of the yoke and the common shunt is also movable circumferentially of the yoke. 

1. Control apparatus for controlling a cathode ray tube of the shadow mask type having several electron guns offset from the central axis of the tube, and a magnetic pole piece integral with each electron gun, comprising an annular main beam deflecting yoke formed to fit round the cathode ray tube; electromagnets, one for each pole piece, so located that they are in magnetic proximity to their respective pole pieces when the apparatus is fitted to the tube, the electromagnets being connected electrically in series with the beam deflecting yoke; and magnetic shunt members movable in field distorting proximity to each of the electromagnets, each shunt member comprising a bar of paramagnetic or diamagnetic material having a tapered leading end.
 1. Control apparatus for controlling a cathode ray tube of the shadow mask type having several electron guns offset from the central axis of the tube, and a magnetic pole piece integral with each electron gun, comprising an annular main beam deflecting yoke formed to fit round the cathode ray tube; electromagnets, one for each pole piece, so located that they are in magnetic proximity to their respective pole pieces when the apparatus is fitted to the tube, the electromagnets being connected electrically in series with the beam deflecting yoke; and magnetic shunt members movable in field distorting proximity to each of the electromagnets, each shunt member comprising a bar of paramagnetic or diamagnetic material having a tapered leading end.
 2. Control apparatus for controlling a cathode ray tube of the shadow mask type having three electron guns spaced round and offset from the central axis of the tube so that, considering one gun as directly above the central axis of the tube, the other two guns are below and on different sides of the central axis, and a magnetic pole piece integral with each electron gun, comprising an annular main beam deflecting yoke formed to fit round the cathode ray tube; electromagnets, one for each pole piece, so located that they are in magnetic proximity to their respective pole pieces when the apparatus is fitted to the tube; and two magnetic shunt members one associated with the electromagnet of the gun above the central axis of the tube and the other associated in common with the electromagnets of the other two guns, both shunt members being movable in field distorting proximity to the associated electromagnets. 